Page 403 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice

Monitoring Fluid Therapy and Complications of Fluid Therapy 393

and fluid requirements for ongoing management. Weight ill small animal patients or may develop as a consequence
gain has been recommended as a monitor of hydration of fluid administration. The endothelium represents a
after fluid therapy, and in my experience, weighing the semipermeable membrane that normally prevents loss
animal has proved to be a useful adjunct of fluid manage- of proteins.
ment.However,weightgaincannotalwaysbepredicted. 29a The COP of whole blood obtained from normal dogs
is 19.95 2.1 (range, 15.3 to 26.3) mm Hg and for
FLUID AND ELECTROLYTE plasma is 17.5 3.0 mm Hg. In whole blood obtained
DISTURBANCES from normal cats, COP is 24.7 3.7 (range, 17.6 to
33.1) mm Hg and in plasma 19.8 2.4 mm Hg.

SERUM ELECTROLYTE
CONCENTRATIONS COMPLICATIONS
Serum electrolyte concentrations require frequent moni-
toring in a patient with a dynamic illness. In the patient POTENTIAL COMPLICATIONS
with hypochloremic alkalosis and hyponatremia ASSOCIATED WITH SELECTION
described previously, caution is required when increasing OF FLUIDS
the sodium content of the fluids administered. In patients Crystalloid Solutions
with serum sodium less than 125 (dogs) to 130 (cats)
mEq/L for greater than 24 hours, an increase of more As previously mentioned, crystalloid fluids should be
than 0.5 mEq/L/hr of sodium may result in a develop- considered drugs because their various compositions will
ment of central nervous system lesions. Similar concerns influence many ionic interactions and shifts in plasma.
exist when attempting to decrease serum sodium concen- The type of fluid selected will influence resolution of alka-
tration in patients with hypernatremia for longer than 24 losis or acidosis. Alkalemia and acidemia will affect the
hours. Serum potassium concentration is influenced by pathologic condition experienced by the animal. If an
acidosis, alkalosis, and the underlying illness, and inappropriate selection is made, such as 0.9% sodium
hyperkalemia or hypokalemia may contribute substan- chloride in a patient with hyperchloremia and decreased
tially to morbidity. Potassium supplementation often is strong ion difference or in another condition resulting
required in many illnesses, but the need for potassium in acidosis, acidosis will worsen, and acidosis has been
supplementation should be carefully evaluated and not shown to increase morbidity. 71 Likewise, in a patient with
assumed. Although abnormalities in serum calcium con- alkalosis, administration of an alkalinizing solution
centration are not as frequent, hypocalcemia and hyper- potentially will contribute to morbidity as electrolyte
calcemia also have diagnostic and therapeutic composition of plasma is altered (e.g., hypokalemia, ion-
implications. Hyperchloremia and hypochloremia can ized hypocalcemia, hyperammonemia), and a shift of the
affect the acid-base status of the patient and warrant vigi- oxyhemoglobin dissociation curve to the left, with
lance and correction as necessary. Hypomagnesemia is a associated problems, occurs. Administration of dextrose
common finding in critical care patients with many also can alter the electrolyte composition of plasma.
underlying illnesses. The electrocardiogram (ECG) may Intracellular shifts of phosphorus and potassium may
be a useful monitoring tool when electrolyte disturbances occur during dextrose infusions, and careful monitoring
exist (e.g., hyperkalemia, hypocalcemia) and result in and supplementation of these ions are required in patients
dysrhythmias; however, one cannot rely on the ECG to with hypophosphatemia and hypokalemia. The addition
diagnose electrolyte abnormalities. For a detailed discus- of dextrose makes the solution more acidic because of
sion on the individual electrolyte disturbances, the reader the oxidation of the sugar. The physiologic acid-base
is referred to the specific chapters in this book. effect of an infusion of 5% dextrose also will be a trend
toward acidosis because of the effective free water infu-
COLLOID OSMOMETRY sion and the effects of glucose metabolism under differ-
Under normal conditions, blood volume and extracellu- ent patient conditions. 80 Another potential concern
lar fluid volume are controlled in parallel to each other. with the administration of 5% dextrose in water is the gen-
However, there are situations in which the distribution eration of free water when additional water is not needed.
of extracellular fluid between the interstitial space and Dextrose-containing solutions may be indicated for spe-
blood can vary. The principal factors that can cause accu- cific situations (i.e., pure water loss).
mulation of fluid in the interstitial space include (1) Lactated Ringer’s solution contains lactate as a bicar-
increased capillary hydrostatic pressure, (2) decreased bonate precursor. Lactate is metabolized in the liver,
plasma COP (oncotic pressure), (3) increased permeabil- and it has been suggested that administration of this fluid
ity of the capillaries, and (4) obstruction of the lymphatic may increase lactate concentration in animals with severe
vessels. 28 With the exception of lymphatic obstruction, liver disease. However, the clinical importance of this
these conditions frequently are preexistent in critically effect must be determined on an individual basis. Mild